- 1 News & Tools
- 2 Subnetting Tutorial & Reference Page
- 3 Standards
- 4 Subnet Zero
- 5 Dynamic Host Configuration Protocol (DHCP)
- 6 ARP (Address Resolution Protocol)
- 7 Neighbor Discovery Protocol (NDP)
- 8 Subnetting Tutorial & Reference Page
- 9 Read / Watch / Do
- 10 Subnetting Tutorial & Reference Page
- 11 Do
- 12 Better Focus and Efficient Studying When Not Multitasking / Multi-Focusing
News & Tools
- Jailed Indian activist was targeted by state-linked hacking group, report says
- IRS to drop facial recognition verification: The IRS announced Monday that the agency “will transition away” from a system that uses third-party facial recognition vendors to verify the identity of people wanting to use its online services. The move comes following an outcry from privacy advocates and lawmakers about reporting related to vendor ID.me’s face-matching system.
- The Red Cross has disclosed that it was the victim of a cyber attack and has asked the hackers who broke into the IT network of one of its contractors not to leak the personal information of more than 515,000 of “highly vulnerable people.” The data was stolen from a Red Cross program called Restoring Family Links, which aims to reunite family members separated by conflict, disaster, or migration.
- Internet Crime Complaint Center (IC3) | Criminals Increasing SIM Swap Schemes to Steal Millions of Dollars from US Public
- FBI: $68 million lost to SIM swapping attacks in 2021
- The Universe is Hostile to Computers (Veritasium)
- Amazon Sidewalk is LIVE – Opt Out Now! – ThreatWire
- Hacker Tries to Poison Water Supply of Florida Town – A threat actor remotely accessed the IT system of the water treatment facility of Oldsmar and raised the levels of sodium hydroxide in the water.
- Hard-to-detect credential-theft malware has infected 1,200 and is still going
- The 5 Challenges of Detecting Fileless Malware Attacks
- RouterSecurity.org focuses on the security of routers.
- PrivacyTools.io provides knowledge and tools to protect your privacy against global mass surveillance.
- RFC (Request for Comments)
- IEEE (Institute of Electrical and Electronics Engineers)
- Deprecated / Deprecation
- The first subnet obtained from subnetting has all bits in the subnet bit group set to zero (0). It is therefore called subnet zero.
- The last subnet obtained from subnetting has all bits in the subnet bit group set to one (1). It is therefore called the all-ones subnet.
- The IETF (Internet Engineering Task Force) discouraged the production use of these two subnets at one point due to possible confusion of having a network and subnet with the same address. The practice of avoiding subnet zero and the all-ones subnet was declared obsolete in 1995 by RFC 1878.
- In this class, we will always include subnet zero when we subnet.
- The process a host uses to get an IP address lease from the DHCP server
- RFC 2131 (Appendix C: DHCP RFCs)
- In addition to an IP address, what additional parameters, if any, does a host need to get from the DHCP server?
- Subnet Mask
- Default Gateway
- DNS Server’s IP address
- DHCP Server uses the UDP port 67 (bootps) and DHCP client uses UDP port 68 (bootpc)
For Phases of DHCP Leasing an IP Address to a Client
|Discover||broadcast –>||Client requests an IP address. |
The client broadcasts a DHCPDISCOVER message on the physical subnet to find available servers. The client creates a UDP packet with the broadcast destination of 255.255.255.255 or the subnet broadcast address.
|Offer||<– unicast||DHCP server offers an IP address from its pool.|
When a DHCP server receives an IP lease request from a client, it extends an IP lease offer. This is done by reserving an IP address for the client and sending a DHCPOFFER message across the network to the client. This message contains the client’s MAC address, followed by the IP address that the server is offering, the subnet mask, the lease duration, and the IP address of the DHCP server making the offer.
|Request||broadcast –>||When the client PC receives an IP lease offer, it must tell all the other DHCP servers that it has accepted an offer. To do this, the client broadcasts a DHCPREQUEST message containing the IP address of the server that made the offer. When the other DHCP servers receive this message, they withdraw any offers that they might have made to the client. They then return the address that they had reserved for the client back to the pool of valid addresses that they can offer to another computer. Any number of DHCP servers can respond to an IP lease request, but the client can only accept one offer per network interface card.|
|Acknowledge||<– unicast||When the DHCP server receives the DHCPREQUEST message from the client, the final phase of the configuration process is initiated. The acknowledgement phase involves sending a DHCPACK packet to the client. This packet includes the lease duration and any other configuration information that the client might have requested. At this point, the IP configuration process is complete.|
- DHCP Scope: A Dynamic Host Configuration Protocol (DHCP) scope is the consecutive/contiguous range/sequence of possible IP addresses the DHCP server can lease to clients on a subnet.
- DHCP Scopes are the primary way for the DHCP server to manage distribution and assignment of IP addresses and any related configuration parameters to DHCP clients on the network.
- Why is ARP on Layer 2 and not on Layer 3 of the OSI Reference Model?
- ARP provides a service to Layer 3
- ARP does not provide Layer 3 services.
- ARP does not use Layer 3 services.
- ARP is not exclusive to IP. ARP is used by other protocols
- ARP is definitely a layer 2 protocol, with Ethernet type = 0x806
- If anyone claims that ARP is on Layer 3, ask them: Does ARP have an IP protocol number?
- ARP Spoofing
Wireshark decode of an ARP Request packet:
- Neighbor Discovery Protocol (NDP) performs functions for IPv6 similar to the way Address Resolution Protocol (ARP) and ICMP Router Discovery and Router Redirect protocols do for IPv4.
- Subnetting Cross-Reference chart
- The “interesting octet” is the last octet in the mask, from left to right, with bits turned on. i.e. 1
- Block Size is the Subnet Increment, not the number of addresses per subnet.
- Using the AND function to determine the network address
- Wildcard Mask
- Broadcast Address
Read / Watch / Do
- Read Chapter 4: Troubleshooting IP Addressing
- Do the Written Labs
- Answer the Review Questions
- Do not submit your answers for this chapter. The answers are in the Appendix.
- How to study effectively: Forget cramming, ditch the highlighter, and stop passively rereading. The psychology of learning offers better tactics. by Paul Penn
Make sure to always have access to a calculator which has an Exponent function (^key) ( xy ) for every class.